1. Field of the Invention
The present invention generally relates to a zoom lens, a camera such as a digital camera, a video camera, a silver-bromide camera or the like, using a zoom lens and a potable information terminal device using the zoom lens.
2. Description of the Related Art
In the related art, a zoom lens has a first lens group having a positive focal length, a second lens group having a negative focal length and an aperture stop member, disposed in this order from the side of an object, and a third lens group disposed on the side of an image from said aperture stop member and having a positive focal length. Such a type of zoom lens is disclosed by Japanese Patent No. 2901144, and so forth.
Further, Japanese Patent No. 2991554 discloses a wide wavelength-range ghost preventing optical system achieving prevention of ghost by using a coating film. Further, Japanese Laid-Open Patent Application No. 07-128501 discloses an imaging optical system reducing ghost flare. In this imaging optical system, reflected light outside of an effective diameter of the lens is reduced.
Such a type of zoom lens as that mentioned above is suitable for miniaturization and achievement of high-power magnification/reduction, and, is used in a video camera and a digital (still) camera, for example. In such a type of zoom lens, for the necessity of aberration correction, the above-mentioned first lens group has a 1-1 negative meniscus lens having a convex surface directed toward an object, a positive 1-2 lens having a surface having a large curvature directed toward the object and joined to the 1-1 lens, and a positive meniscus 1-3 lens having a convex surface directed toward the object, disposed in this order from the object, in many cases.
Further, with regard to such an image-pickup and imaging optical system, this system has a problem of ghost flare. Especially, such a type of ghost flare as that in which reflected light reflected between two lenses reaches an image surface even through the light source does not exist within the screen may occur depending on the configuration of lenses.
An object of the present invention is to solve the above-mentioned problems. Specifically, an object of the present invention is to provide a such a type of zoom lens as that mentioned above in which the above-mentioned type of ghost flare as that generated as a result of reflected light reflected between two lenses reaching an image surface can be reduced.
A zoom lens according to the present invention includes a first lens group having a positive focal length, a second lens group having a negative focal length, an aperture stop member, a third lens group having a positive focal length, disposed in the stated order from the side of an object. The above-mentioned first lens group includes a negative meniscus 1-1 lens having a convex surface directed toward the object, a positive meniscus 1-2 lens having a convex surface having a large curvature directed toward the object and joined with the 1-1 lens, and a positive meniscus 1-3 lens having a convex surface directed toward the object, disposed in the stated order from the side of the object. Further, a reflection preventing measure is formed on a surface at which the 1-1 lens and said 1-2 lens are joined.
Thereby, it is possible to reduce such a type of ghost flare as that generated as a result of reflected light reflected between two lens surfaces of the zoom lens reaching an image surface. Accordingly, even in a case of taking a picture against the (sun) light through a video camera or a digital camera employing the zoom lens, it is possible to take a high-quality picture.
The reflection preventing measure may comprise a coating film formed only on one of a second surface of the 1-1 lens and a first surface of the 1-2 lens having a higher refractive index of lens material.
Thereby, it is possible to effectively reduce the ghost light through a simple configuration at low costs.
The reflection preventing measure may comprise coating films formed both on the second surface of the 1-1 lens and on the first surface of the 1-2 lens, respectively.
Thereby, it is possible to provide the zoom lens in which the ghost flare is effectively reduced even in a design such that aberration correction is performed with high priority. Accordingly, it is possible to achieve a miniaturized, value added, such as wide-range size-variable, video camera or digital camera rendering high image quality even in a case of taking a picture against the (sun) light.
The reflection preventing measure may comprise an adhesive layer having a high refractive index na used for joining the 1-1 lens and the 1-2 lens together, wherein:
na greater than 1.60
Thereby, it is possible to provide the zoom lens in which the ghost light is effectively reduced without increasing the number of steps of manufacturing process of the zoom lens. Accordingly, it is possible to provide a miniaturized, value added, such as wide-range size-variable, digital camera or video camera at low costs.
The following formula may be satisfied:
(|n1-1xe2x88x92na|+|n1-2xe2x88x92na|)/2 less than 0.21
where n1-1 denotes a refractive index of the 1-1 lens and n1-2 denotes a refractive index of the 1-2 lens.
Thereby, it is possible to provide the zoom lens in which the ghost flare is reduced more effectively. Accordingly, it is possible to provide a digital camera or a video camera in which an image quality of a picture taken against the (sun) light is further improved.
A multi-coating film may be formed on the first surface of the 1-1 lens.
Thereby, it is possible to provide the zoom lens in which the ghost flare can be reduced more effectively. Accordingly, it is possible to provide a video camera or a digital camera which can be used against the (sun) light with a higher performance.
A camera according to the present invention employs one of the above-mentioned zoom lens according to the present invention as an image pickup lens thereof. This camera may comprise a normal silver-bromide camera, or a camera having a function of generating digital information from a picked-up image, such as a digital still camera, a digital video camera, and so forth. Accordingly, such a camera may comprise a portable information terminal device which can transmit such digital information externally through the Internet or the like.